1. Field of the Invention
The present invention generally relates to a light emission control circuits and, more particularly, to a circuit for controlling light emission of light-emitting devices for illumination of a liquid crystal panel.
2. Description of the Related Art
Liquid crystal display apparatuses are widely used in portable terminals such as a notebook personal computer. A liquid crystal panel in a liquid crystal display apparatus is illuminated from behind by a backlight so that desired display is obtained as a result of blocking and transmission of light caused by interaction between a liquid crystal and a polarizing filter. A liquid crystal display apparatus is generally known for its low power consumption and will continue to be one of the key display apparatuses.
A line light source such as a fluorescent tube, which is usually capable of illuminating the entirety of a panel at an equal level, is used in a personal computer due to the availability of a substantially sufficient amount of space for a light source. In a portable terminal, however, there is a need to avoid a light source that requires an excessively large housing space or an extremely high lighting voltage. For this reason, many portable terminals today use light-emitting diodes capable of being lighted at a relatively low voltage. Japanese Patent Laid Open Publication 2000-180850 proposes a structure of a liquid crystal display apparatus using the diode.
An idea should be introduced in order to allow the light emitted by light-emitting diodes to reach the entirety of a panel at an equal level. Japanese Patent Laid Open Publication mentioned above discloses reduction of ununiformity of light using a light guide panel but does not, however, discloses how the degree of ununiformity is managed nor does it disclose taking into account unit-to-unit variation or time-dependent change of a light source. Granting that the light is controlled to be uniform, the disclosure in the patent document overlooks too high or too low an overall luminance level. A combination of red (R), green (G) and blue (B) light-emitting diodes to provide backlight is not capable of desirable light emission unless a proper luminance balance is achieved. The patent document is also silent as to how the luminance balance is managed.
Related Art List
JPA laid open 2000-180850